The assembly is already known of a pressurized fluid motor having at least two distinct operational cubic capacities, comprising a driven member, such as a driving shaft, and of a brake coupled to said driven member of the pressurized fluid motor, said pressurized fluid motor, such as a hydraulic motor, being capable of being placed in two distinct configurations, the first corresponding to a large operational cubic capacity and, for a determined value of the pressure of the supply fluid, to a high driving torque, and the second configuration corresponding to a small operational cubic capacity, less than said large operational cubic capacity, and, for said determined value of the pressure of the supply fluid, to a low driving torque, less than said high driving torque, said pressurized fluid motor further comprising a cubic capacity selector having a mobile member with at least two positions, the first of the two positions placing the pressurized fluid motor in its first configuration and the second position placing it in the second configuration, said mobile member being coupled to a first elastic return means which tends to place it in its second position and to a first pressurized fluid jack capable of being supplied with fluid under pressure, whose effect is antagonistic of that of said first elastic return member, whilst the brake comprises a braking control device, which comprises at least two positions, and which is coupled, on the one hand, to a second member for return into braking position, on the other hand, to a second jack, of antagonisitc effect, comprising a braking-release chamber capable of being placed in communication with a source of fluid under pressure, said braking control member presenting two particular positions, a first corresponding to the action of braking and to the predominance of the return effect of the second return member, and a second position corresponding to the effective placing in communication of the braking-release chamber with a source of pressurized fluid, to the predominance of the effect of the second jack and to braking-release control.
According to the known art, there is a risk of a user switching on the motor whilst the latter is placed in the configuration of its large cubic capacity, therefore for obtaining the high driving torque, without controlling braking release.
The braking torque developed by the brake is sufficient to maintain the vehicle immobile or to stop it if necessary--it is generally a hand--and safety brake--but is less than the high driving torque. In that case, the erroneous manoeuvre of the user firstly does not prevent the motor from driving the vehicle, which is a risk of accident, particularly of persons, and also causes the brake linings to rub on the mobile member of the brake, which overheats them, leading to deterioration thereof.
It is possible to overcome these drawbacks by choosing a brake developing a braking torque greater than the high driving torque. This solution leads to the choice of a brake which is much more cumbersome and expensive than a conventional hand--and safety brake.
It is an object of the present invention to remedy this state of affairs by providing that, as long as the brake is in its braking configuration, the motor is automatically placed in its configuration of small cubic capacity, therefore of low driving torque. In that case, it suffices to choose a brake of which the braking torque is greater than said low driving torque so that any untimely drive of the vehicle, with the brake applied, is avoided.